1. Field of the invention
The invention relates generally to methods for manufacturing carbon nanotubes; and more particularly to a method for manufacturing carbon nanotubes with a uniform length.
2. Description of Related Art
Carbon nanotubes have interesting electrical, magnetic, nonlinear optical, thermal, and mechanical properties, and these unusual properties have led to diverse potential applications for carbon nanotubes in materials science and nanotechnology. For example, in an article entitled “Unusually High Thermal Conductivity of Carbon Nanotubes” and authored by Savas Berber (page 4613, Vol. 84, Physical Review Letters 2000), it is shown that a heat conduction coefficient of a carbon nanotube can be 6600 W/mK (watts/milliKelvin) at room temperature. One important application of carbon nanotubes is to form a thermal interface material by incorporating a plurality of carbon nanotubes in a matrix material. This application utilizes the excellent heat conduction coefficient of the carbon nanotubes.
Other applications involve the use of freestanding carbon nanotubes, especially freestanding carbon nanotubes having a uniform length. At present, the most notable method for manufacturing carbon nanotubes having a uniform length is chemical vapor deposition. The length of the carbon nanotubes manufactured by this method can be controlled to some extent by controlling the growth time. However, the precision of length control is low. Furthermore, once the carbon nanotubes have been grown, their length is fixed and they cannot be trimmed. If the length is not the desired length, a completely new batch of carbon nanotubes must be grown. Another method for obtaining carbon nanotubes having a uniform length utilizes the technology of making thermal interface materials. This is because in some thermal interface materials, the carbon nanotubes in the matrix have a uniform length. Therefore once the thermal interface material is made, the desired carbon nanotubes can be extracted therefrom.
U.S. Pat. No. 6,407,922 discloses a thermal interface material comprising a matrix material and a plurality of carbon nanotubes incorporated in the matrix material. A first surface of the thermal interface material engages with an electronic device, and a second surface of the thermal interface material engages with a heat sink. The second surface has a larger area than the first surface, so that heat can be uniformly spread over the larger second surface.
In this application of the thermal interface material, the carbon nanotubes are required to have a uniform length to ensure that the thermal interface material has uniform physical characteristics. However, in practice, the uniformity of length obtained is not precise.
A new method for manufacturing carbon nanotubes which overcomes the above-mentioned problems is desired.